Wrought aluminum base alloy product having refined Al-Fe type intermetallic phases

ABSTRACT

A wrought aluminum alloy product is disclosed. The alloy consists essentially of 0.5 to 10 wt. % Mg, 0.3 wt. % max. Mn, 0 to 0.35 wt. % Cr, at least 0.005 wt. % Sr, less than 1 wt. % Fe, 0.3 wt. % max. free Si, 3.5 wt. % max. Zn, 1 wt. % max. Cu, 0.3 wt. % max. Ti, the remainder aluminum and incidental impurities. The product is characterized by the presence of an intermetallic phase of the type containing Al-Fe in a refined condition.

INTRODUCTION

This invention relates to aluminum alloys and more particularly itrelates to wrought aluminum alloy products such as sheet products.

In the fabrication of aluminum alloy substrates for memory discs,normally the substrates are machined usually on both sides prior toapplying a coating thereto which functions as memory medium. It will beappreciated that for use as a memory disc substrate, the surface has tobe extremely smooth in order not to interfere with the coatings and forstorage of information therein. Normally, information is stored in suchcoating by electrical impulses or magnetized spots where presence orabsence of such represent data and accordingly, it will be seen thatirregularities in the surface can interfere with the ability of thecoating to retain data accurately. The machining step referred to hasnot been without problems. For example, in some of the alloys used,insoluble constituents have presented problems from a machiningstandpoint, resulting in a high rejection rate for the substrates. Thatis, it has been found that in certain aluminum base alloys, insolubleconstituents such as Al-Fe-Mn-Si constituents or phases, form in ratherlarge particle sizes, sometimes greater than 1 micron, and interferewith the machining operation, particularly that required in thepreparation of substrates for memory discs. These constituents caninterfere with the machining operation by catching on the cutting tooland being removed therewith or being pulled across the machined surfaceleaving scratches. In either case, it adversely affects the smoothnessdesired. Further, it is believed that when a machined surface is etched,the large constituents interfere with uniformity of etching.

Even if the surface has been found to machine adequately, there can beinstances where the coating or undercoating therefor is interfered withto an extent which affects storage of data in the coating. Theinterference is believed to result from relatively large intermetallicphases or constituents as noted above. Thus, it can be seen that suchphases or constituents must be provided in a refined or modifiedcondition which provides freedom from such conditions.

In addition, it has been found that such or similar problems can arisewhen aluminum-based alloys are anodized for use as bright trim onautomobiles. That is, these intermetallic constituents can resistetching and anodization treatments resulting in holes or unanodizedspots in the protective anodic coating which, of course, can severelyinterfere with the useful service life of the trim. Thus, again, it canbe seen that it is very important to provide the intermetallic phases orinsoluble constituents in a refined or modified condition which avoidsthese problems. Similarly, with fine wire forming, such as screen wire,the large particles interfere with the forming operation. That is, thelarge particles can cause severe breakage problems, in wire drawing. Itwill be understood that the problems referred to are used more forillustrative purposes and that there are many other applications whererelatively large particle constituents interfere with the use of theparticular aluminum alloy.

The present invention provides an aluminum base alloy wrought producthaving a refined or modified intermetallic phase or insolubleconstituent which may be machined to a smoothness suitable for use asmemory disc substrates, for example. In addition, aluminum base alloyproducts, e.g. extrusion or sheet-type products, in accordance with theinvention have, inter alia, enhanced anodizing characteristics.

OBJECTS

A principal object of this invention is to provide an improved wroughtaluminum base alloy product.

Another object of this invention is to provide a wrought aluminum alloybase sheet product having enhanced machining characteristics and beingsuitable for memory disc substrates.

A further object of this invention is to provide a wrought aluminumalloy base product characterized by refinement or modification ofintermetallic phases.

And yet a further object of this invention is to provide a wroughtaluminum alloy base sheet product having a refined or modifiedintermetallic phase of the Al-Fe type.

These and other objects will become apparent from the specification,drawings and claims appended hereto.

SUMMARY OF THE INVENTION

In accordance with these objects, a wrought aluminum sheet product isprovided. The sheet product contains essentially 0.5 to 10 wt.% Mg, 0.3wt.% max. Mn, 0 to 0.35 wt.% Cr, at least 0.005 wt.% Sr, less than 1wt.% Fe, 0.3 wt.% max. free Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, theremainder aluminum and incidental impurities and is characterized by atleast one of refinement and modification of an intermetallic phasecontaining Al-Fe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photomicrograph (500X) of an aluminum base alloy sheetproduct showing constituent particles of Al-Fe-Mn-Si which interferewith machinability of the sheet.

FIG. 2 is a photomicrograph (500X) of an aluminum base alloy sheetproduct of FIG. 1 having refined or modified constituent particles, thesheet product having improved machining characteristics and beingparticularly suitable for memory disc substrates.

FIG. 3 is a photomicrograph (500X) of the aluminum base alloy of FIG. 2,except the sheet product is provided in a thinner gauge.

FIG. 4 is a phase diagram showing the relationship of intermetallicphases and compositions of an aluminum base alloy containing 0.2 wt.% Feafter a soak period at 950° F.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In certain aluminum base alloys, because of advances in the technologyin which the alloy is used, it has become necessary to refine theconstituent particle size in order to permit use of the new technology.For example, in disc-storage technology, efforts have been made toincrease the amount of data which can be stored on a single disc and toswitch the medium traditionally used for storage purposes in order tocircumvent problems. Efforts have been made to switch from ironoxide-type memory medium in order to increase the medium's resistance toerasure. Thin surface layers of cobalt, for example, have beeninvestigated quite successfully to determine its suitability for suchapplications. Applications of a layer of memory medium such as ironoxide to an aluminum substrate involve different technology and thickerlayers than that used for applying the thin layer of cobalt, forexample. For instance, the iron oxide medium is applied to the substrateas a slurry or dispersed in a plastic binder, whereas plating or otherforms of deposition, e.g. vapor or vacuum deposition, can be used forapplying thin, metallic layers such as the thin cobalt layers. Inaddition, the thin metal films are very sensitive to defects on thesurface of the aluminum substrate to which it is applied. For example,large constituent particles can interfere with the plating or depositionof the thin metallic layer. Also, as noted earlier, the large particlescan interfere with the smoothness of the finish attainable on thealuminum substrate by machining, which in turn, is reflected inroughness of the thin metallic film deposited on the substrate. It mustbe rembered that particles, e.g. dust particles of about 0.3 micron, caninterfere with the effectiveness of the head used for storing or readingdata from the medium layer, particularly where the medium layer iscomprised of a thin metallic layer. Accordingly, it can be seen why itis so important to minimize roughness on the surface of the aluminumsubstrate on which the layer is deposited.

Similarly, such problems with large constituent particles can beencountered in anodization of aluminum alloys used for auto trim, forexample. That is, the constituent particle on or near the surface canreact or oxidize quite differently from surrounding material resultingin defects in the anodic coating. Such defects can adversely affect thecorrosion resistance of the anodic coating on the trim. Thus, in the twoexamples given, it can be seen that such particles are best avoided.

FIG. 1 is a photomicrograph of an aluminum base alloy which has beenused for memory disc substrates where the memory laser consistedparticularly of iron oxide applied by the slurry. The alloy contains0.20 wt.% Fe, 0.11 wt.% Si, 0.37 wt.% Mn, 4.06 wt.% Mg, 0.02 wt.% Cu,0.08 wt.% Cr, 0.02 wt.% Zn and 0.01 wt.% Ti, the remainder aluminum andimpurities. However, as can be seen from the micrograph, rather largeAl-Fe-Mn-Si constituent particles occur throughout the metal. Some ofthe particles are on the order of about 1 micron which, as notedearlier, can interfere with machining and consequently with the memorymedium.

FIG. 2 shows a photomicrograph of a wrought aluminum sheet product,particularly suitable for memory disc substrates, in accordance with theinvention. The alloy of FIG. 2 contains 0.22 wt.% Fe, 0.18 wt.% Si, 0.40wt.% Mn, 3.85 wt.% Mg, 0.08 wt.% Cr, 0.033 wt.% Sr, 0.02 wt.% Zn, 0.03wt.% Cu and 0.01 wt.% Ti, the remainder aluminum and incidentalimpurities. Inspection of the micrograph reveals the absence ofconstituent particles having a size compared to that shown in FIG. 1. Itis the freedom from relatively large particles which interfere withmachining that provides the wrought sheet product shown in FIG. 2 withsuperior characteristics. Also, it is the absence of large particleswhich makes the product highly suitable for substrates such as thoseused in memory discs, particularly where the memory medium is a thinlayer or film of metallic material which is plated or deposited on thesubstrate. Further, in compositions or alloys in accordance with theinvention, the absence of such large particles makes the extrusionproduct, e.g. auto trim, as well as sheet product particularly suitablefor anodizing. The sheet products of FIGS. 1 and 2 were rolled to0.162-inch gauge. However, even when the sheet product of FIG. 2 isrolled to a sheet thickness of 0.082 inch gauge, it still retains itsrefined or modified structure, as can be seen by examination of thephotomicrograph of FIG. 3.

When a wrought product in accordance with the invention is desired, thealloy can consist essentially of 0.5 to 9 wt.% Mg, 0.1 to 1.4 wt.% Mn, 0to 0.35 wt.% Cr, 0.005 to 2.5 wt.% Sr, less than 1 wt.% Fe, 1 wt.% max.Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, the remainder aluminum andincidental impurities.

Magnesium is added or provided in this class of aluminum alloys mainlyfor purposes of strength and is preferably maintained in the range of0.5 to 5.6 wt.%. Magnesium is also useful since it promotes finealuminum grain size in the alloy which, of course, aids formability. Itshould be noted, though, that higher levels of magnesium can lead tofabrication problems. Thus, it becomes important to balance thestrengths desired against problems in fabrication. With respect tomachining, the higher levels of magnesium in solid solution favormachinability. Aluminum alloys having the poorest machiningcharacteristics have a low alloy content and are usually in the annealedor softest condition. Conversely, increasing alloy concentration, coldwork, solution and aging treatments, result in an improved surfacefinish by hardening the alloy, by reducing adherence of metal to thetools and by reducing the number of burrs. That is, these additions ortreatments improve machinability. Thus, for purposes of machiningaluminum alloy substrates for memory discs, it is desirable to maintainthe magnesium in the range of about 3.5 to 5.5 wt.%. Where theapplication is aluminum screen wire, which is drawn to a very finediameter, magnesium should be in the range of 4.5 to 5.6 wt.%, and wherethe application is aluminum easy-open-ends for beverage containers andthe like, magnesium should be in the range of 4 to 5 wt.%. While higherlevels of magnesium have been referred to for purposes ofexemplification, lower levels of magnesium are also important in certainapplications such as alloys used for rigid containers, trim,architectural products, trucks and railroad vehicles and arecontemplated to be within the purview of the invention.

With respect to manganese, preferably it is maintained to less than 1wt.%, and typically it is maintained in the range of 0.1 or 0.2 to 0.8wt.%. Manganese is a dispersoid forming element. That is, manganese isan element which is precipitated in small particle form by thermaltreatments and has, as one of its benefits, a strengthening effect.Manganese can form dispersoid consisting of Al-Mn, Al-Fe-Mn andAl-Fe-Mn-Si. Thus, in some magnesium-containing alloys where it isdesired to increase corrosion resistance, magnesium can be lowered andmanganese added at no loss in strength, but with increased resistance tocorrosion. Likewise, chromium can have the advantage of increasingcorrosion resistance, particularly stress corrosion. Also, chromium cancombine with manganese to provide more dispersoid which, as notedearlier, can increase strength. Chromium can also have an effect byinfluencing preferred orientation with respect to earing, in cups forexample. It will be understood that earing is detrimental because itresults in wastage of metal. Preferably, chromium should not exceed 0.25wt.% for most of the applications for which alloys of the invention maybe used.

Solid solubility of iron in aluminum is very low and is on the order ofabout 0.04 to 0.05 wt.% in ingot. Thus, normally a large part of theiron present is usually found in aluminum alloys as insolubleconstituent in combination with other elements such as manganese andsilicon, for example. Typical of such combinations are Al-Fe-Mn,Al-Fe-Si and Al-Fe-Mn-Si. It will be appreciated that the elements inthese combinations can be present in various stoichiometric amounts. Forexample, Al-Fe-Si can be present as Al₁₂ Fe₃ Si and Al₉ Fe₂ Si₂ whichare considered to be the most commonly occurring phases. Also, Al-Fe-Mncan be present as Al₆ (Fe_(x) Mn_(1-x)), where x is a number greaterthan 0 and less than 1. With respect to Al-Fe-Mn-Si, this combinationcan be present as Al₁₂ (Fe_(x) Mn_(1-x))₃ Si, where x is a numbergreater than 0 and less than 1. It should be noted that theseconstituents are considered to be the most common intermetallic phasesfound in these types of alloys. However, it should be understood thatother elements such as Cu, Ti and Cr and the like can appear in or enterinto the intermetallic phases referred to in minor amounts bysubstituting usually for part of the Fe or Mn. Such intermetallic phasesare also contemplated within the purview of the invention. Theseinsoluble constituents tend to agglomerate and form relatively largeparticles such as Al-Fe-Mn-Si constituents, as may be seen in FIG. 1,some of which are approximately 1 micron in length. As noted earlier, itis these larger, insoluble constituents that are so undesirable from thestandpoint of machinability and formability. However, it must beremembered that iron has a beneficial effect as a grain refiner which,of course, aids machinability and formability. Further, it must beunderstood that iron is normally present in most aluminum alloys, mainlyfrom an economic standpoint. That is, processing aluminum to remove ironfor most applications is normally not economically feasible. Thus, manyattempts have been made to work with iron in the alloy by takingadvantage of its benefits and neutralizing its disadvantages often withonly limited success. Thus, preferably, for purposes of the presentinvention, iron is maintained at 0.8 wt.% or lower, and typically lessthan 0.5 wt.%, with amounts of 0.4 wt.% or less being quite suitable.

Titanium also aids in grain refining and should be maintained to notmore than 0.2 wt.%.

For purposes of the present invention, it is believed that the amount ofsilicon also should be minimized since, at relatively low levels it cancombine with magnesium, resulting in significant strength reductions.Thus, preferably, silicon should be maintained at less than 0.5 wt.% andtypically less than 0.35 wt.%.

Strontium, which should be considered to be a character-forming element,is also an important component in the alloys of the present invention.Strontium must not be less than 0.005 wt.% and preferably is maintainedin the range of 0.005 wt.% to 0.5 wt.% with additional amounts notpresently believed to affect the performance of the products adversely,except that increased amounts may not be desirable from an economicstandpoint. For most applications for which alloys of the prsentinvention may be used, strontium is preferably present in the range of0.01 wt.% to 0.25 wt.%, with typical amounts being in the range of 0.01wt.% to 0.1 wt.%.

The addition of strontium to the composition has the effect of refiningor modifying intermetallic phases or insoluble constituents of the typecontaining Al-Fe-Si, Al-Fe-Mn and Al-Fe-Mn-Si as noted earlier. Becauseof the complex nature of these phases, it is not clearly known how thiseffect comes about. That is, because of the multiplicity of alloyingelements and the interaction with each other, it is indeed quitesurprising that a significant refinement of insoluble constituent isobtained.

However, the benefit of adding strontium can be clearly seen bycomparing the micrographs of wrought sheet products shown in FIG. 1, 2or 3. The compositions for these sheet products were providedhereinabove. The ingot from which these sheet products were rolled wascast by the direct chill method. An ingot having this composition wasfirst scalped, homogenized for 2 hours at 1050° F., and then, startingat about a temperature of 950° F., hot rolled to a thickness of about0.182 inch. From an examination of FIG. 1, it will be seen that some ofthe Al-Fe-Mn-Si particles or insoluble constituents are relatively largeand have lengths of about 1 micron. FIG. 2 is a micrograph (500X) of analloy having the same composition as that shown in FIG. 1 except 0.02wt.% strontium was added. The alloy was rolled in the same way as forthe alloy of FIG. 1. It will be seen that the Al-Fe-Mn-Si particles aregreatly reduced in size when compared to FIG. 1. Also, the insolubleconstituents including the dispersoid phase have a substantially uniformdistribution throughout the matrix. Thus, it will be observed that thestrontium has the effect of refining the intermetallic phases.

Even if the sheet product of FIG. 2 is further cold rolled to 0.082 inchgauge after annealing, the small insoluble constituent or intermetallicphases are maintained. For example, FIG. 3 is a micrograph (500X) of analuminum base alloy having the same composition and fabricated in thesame way as FIG. 2, except that it was rolled to 0.082 inch gauge. Aswill be observed from FIG. 3, the fine particle constituent wasmaintained. Thus, from these micrographs it will be seen that strontiumhas the effect of refining these intermetallic phases in the alloy andmaintaining the refined condition after the alloy has been fabricatedinto a wrought sheet product, for example.

An x-ray diffraction analysis using a Guinier-type camera of the sheetsamples referred to in FIGS. 1, 2 and 3 shows the relative amounts ofthe intermetallic phases present. The results of the analysis aretabulated in the following Table.

                                      TABLE                                       __________________________________________________________________________    Mg.sub.2 Si                                                                            Al.sub.12 (Fe.sub.1 Mn.sub.3)Si                                                       Al.sub.12 (Mn.sub.1 Fe.sub.3)Si                                                       (FeMn)Al.sub.6                                                                      FeAl.sub.3                                                                        Cr.sub.2 Al.sub.11                         __________________________________________________________________________    Alloy of                                                                           small+                                                                            small+  --      small-                                                                              very                                                                              possible                                   FIG. 1                         small+                                                                            trace                                      Alloy of                                                                           small                                                                             medium- very small                                                                            trace --  --                                         FIG. 2                                                                        Alloy of                                                                           small+                                                                            medium- very small                                                                            very small                                                                          --  --                                         FIG. 3                                                                        __________________________________________________________________________

As well as providing the wrought product in compositions havingcontrolled amounts of alloying elements as described above, it ispreferred that compositions be prepared and fabricated into productsaccording to specific method steps in order to provide the mostdesirable characteristics. Thus, the alloys described herein can beprovided as an ingot or billet or can be strip cast for fabrication intoa suitable wrought product by techniques currently employed in the art.The cast material, such as the ingot, may be preliminarily worked orshaped to provide suitable stock for subsequent working operations. Incertain instances, prior to the principal working operation, the alloystock may be subjected to homogenization treatment and preferably atmetal temperatures in the range of 800° F. to 1100° F. for a time periodof at least 1 hour to dissolve magnesium or other soluble elements andto homogenize the internal structure of the metal and in some cases toprecipitate dispersoids. A preferred time period is 2 hours or more athomogenization temperature. Normally, for ingot the heatup andhomogenizing treatment do not have to extend for more than 24 hours;however, longer times are not normally detrimental. A soak time of 1 to12 hours at the homogenization temperature has been found quitesuitable.

After the homogenizing treatment, the metal can be rolled or extruded orotherwise subjected to working operations to produce stock such asplate, sheet, extrusion or wire or other stock suitable for shaping intothe end product. To produce a sheet-type product, a body of the alloy ispreferably hot rolled to a thickness in the range of about 0.125 to 0.25inch. For hot rolling purposes, the temperature should be in the rangeof 600° F. to about 1050° F. and preferably the temperature initially isin the range of 850° F. to 950° F. The temperature at completion ispreferably 400° F. to 600° F.

When the intended use of a selected composition is a typical wroughtsheet product such as is suitable for memory disc substrates, forexample, final reduction as by cold rolling can be provided. Suchreduction can be to sheet thicknesses in the range of 0.058 to 0.162inch. The disc substrates may then be stamped from the sheet andthermally flattened at a temperature in the range of 350° F. to 750° F.for a period of time of 1 to 5 hours with a typical flattening treatmentbeing 3 to 4 hours at 425° F. to 650° F. under pressure. The substratesare usually rough cut and then precision machined to remove about 0.006inch in order to obtain the proper degree of flatness and smoothnessbefore applying the memory medium. After machining it may be desirableto thermally flatten the substrates again. In addition, after machining,normally the substrates should be degreased and given a light etchingtreatment. Prior to applying the memory medium, the substrates may begiven a chemical conversion treatment, particularly if the ironoxide-type memory medium is used.

In certain applications, depending on the properties required, it may bedesirable to subject the product after working to a thermal treatment.This treatment may be provided as an intermediate anneal or after theproduct has been worked to final dimensions. For a partial anneal, thetemperature is usually in the range of 200° F. to 500° F. with a typicalrange being about 300° F. to 500° F. for time periods in the range ofabout 1 to 4 hours. For full anneal, generally the temperature is in therange of 600° F. to 775° F. for most applications with typical annealingpractices normally being in the range of 650° to 750° F. For fullanneal, time at annealing temperature is in the range of 1 to 2 hoursfor batch material.

When the intended use of the wrought product in accordance with theinvention is screen wire, for example, preferably the alloy consistsessentially of 4 to 5.6 wt.% Mg, 0.05 to 0.2 wt.% Mn, 0.05 to 0.2 wt.%Cr, not less than 0.005 wt.% Sr, 0.4 wt.% max. Si, 0.4 wt.% max. Fe, 0.1wt.% max. Cr, 0.25 wt.% max. Zn, the remainder aluminum and incidentalimpurities. Additional impurities should not constitute more than 0.15wt.% total. When the intended use of the wrought sheet product is truckbody panels and the like, for example, the alloy can consist essentiallyof 2.2 to 2.8 wt.% Mg, 0.1 wt.% max. Mn, 0.15 to 0.35 wt.% Cr, 0.005 to0.25 wt.% Sr, 0.25 wt.% max. Si, 0.4 wt.% max. Fe, 0.1 wt.% max. of bothCu and Zn, the balance aluminum and impurities, the total of impuritiesnot exceeding 0.15 wt.%. In instances where higher strengths may berequired, such as in tank cars and the like, while maintainingweldability and formability, manganese may be increased in the latteralloy to be in the range of 0.5 to 1 wt.%. Likewise, where high degreesof strength are required, such as in armor plate or in liquefied naturalgas containers, magnesium can be increased to be in the range of 4 to4.9 wt.%.

In another aspect of the invention, it may be desirable to control theamount of manganese in the alloy composition in accordance with theinvention to not greater than 0.3 wt.%. This may be desirable where thesheet product is to be used for easy-open-ends, for example. The phasediagram of FIG. 4 shows the relationship of compositions and phases whenmanganese is in the range of 0 to 0.3 wt.% and free silicon is less than0.3 wt.% in aluminum base alloy compositions having 0.2 wt.% Fe. In thephase diagram, the area referred to as 1 denotes that the onlyintermetallic phase obtained is the Al-Fe type phase such as FeAl₃ orthe metastable phase FeAl₆. Similarly, in the area denoted as 2, theintermetallic phases of the Al-Fe and Al-Fe-Mn [e.g. (FeMn)Al₆)] areobtained. The following tabulation identifies the intermetalliccompounds found in the different areas of the phase diagram:

    ______________________________________                                        Area    Intermetallic Compounds                                               ______________________________________                                        1       FeAl.sub.3                                                            2       FeAl.sub.3 + (FeMn)Al.sub.6                                           3       FeAl.sub.3 + (FeMn)Al.sub.6 + Al.sub.12 (FeMn).sub.3 Si               4       (FeMn)Al.sub.6                                                        5       (FeMn)Al.sub.6 + Al.sub.12 (FeMn).sub.3 Si                            6       FeAl.sub.3 + Al.sub.12 (FeMn).sub.3 Si                                7       Al.sub.12 (FeMn).sub.3 Si                                             8       Al.sub.12 (FeMn).sub.3 Si + Al.sub.12 (MnFe).sub.3 Si                 9       Al.sub.12 (FeMn).sub.3 Si + Al.sub.12 (MnFe).sub.3 Si                         + (FeMn)Al.sub.6                                                      ______________________________________                                    

The addition of strontium in the composition can have the effect ofrefining or modifying the Al-Fe phase when the composition with respectto Mn and free Si is maintained within these limits. By free Si is meantthat in Mg-containing aluminum alloys, the silicon is not combined ortied up with Mg. However, such Si may be combined with Mn, Fe, or both.With respect to the phase diagram, it will be noted that no Mg ispresent since its effect would be to lower the free silicon content.

The phase diagram was developed as follows. A series of alloys wasprepared containing refined aluminum with 0.2% Fe. Mn was added toprovide 0.1, 0.2, 0.3 and 0.5 wt.% and Si was added to provide from 0 to1 wt.%. Master alloys with 0% Si and 1% Si were made as 2500 gramcharges cast as notch bar. Intermediate Si contents were made bycombining the master alloys. 200 gram charges were melted and cast as1/4×2×4 inch ingots in molds preheated at 600° F. The ingots were cutinto 1-inch squares for preheat experiments. They were programmed 50°F./hr to 850° F., 950° F., 1050° F. or 1125° F., held 16 hours attemperature and quenched to retain phases present at the preheattemperature. Phases were identified in the specimens by x-raydiffraction and the results were used to construct the phase diagram.

The phase diagram shows that Al-Fe type intermetallic is the primaryintermetallic phase present in the area denoted as 1 and that this phaseis also present in the areas denoted as 2, 3 and 6.

While the invention has been described in terms of preferredembodiments, the claims appended hereto are intended to encompass otherembodiments which fall within the spirit of the invention.

What is claimed is:
 1. A wrought aluminum alloy product, the alloyconsisting essentially of about 2.2 to 10 wt.% Mg, 0.3 wt.% max. Mn, 0to 0.35 wt.% Cr, 0.005 to 2.5 wt.% Sr, 0.04 to 1 wt.% Fe, 0.3 wt.% max.free Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, 0.3 wt.% max. Ti, theremainder aluminum and incidental impurities, the product beingcharacterized by the presence of an intermetallic phase of the typecontaining Al-Fe in a refined condition.
 2. The product in accordancewith claim 1 wherein Mg is maintained in the range of about 2.2 to 5.6wt.%.
 3. The product in accordance with claim 1 wherein Mg is maintainedin the range of 3.5 to 4.5 wt.%.
 4. The product in accordance with claim1 wherein Mn is 0.2 wt.% max.
 5. The product in accordance with claim 1wherein Fe is less than 0.5 wt.%.
 6. The product in accordance withclaim 1 wherein free Si is less than 0.1 wt.%.
 7. The product inaccordance with claim 1 wherein Sr is maintained in the range of 0.01 to0.25 wt.%.
 8. A wrought aluminum alloy sheet product, the alloyconsisting essentially of about 2.2 to 5.6 wt.% Mg, 0.3 wt.% max. Mn,0.25 wt.% max. Cr, 0.005 to 0.5 wt.% Sr, 0.04 to 0.5 wt.% Fe, 0.3 wt.%max. Ti, 0.2 wt.% max. free Si, 3.5 wt.% max. Zn, 1 wt.% max. Cu, theremainder aluminum and incidental impurities, the product beingcharacterized by the presence of at least one intermetallic phase of thetype containing Al-Fe in a refined condition.